The traditional reliability of telecommunication systems that users have come to expect and rely upon is based in part on the systems' operation on redundant equipment and power supplies. Telecommunication switching systems, for example, route tens of thousands of calls per second. The failure of such systems, due to the loss of incoming AC power, is unacceptable since it would result in a loss of millions of telephone calls and a corresponding loss of revenue.
Power plants, such as battery plants, address the power loss problem by providing the system with a backup power supply for use in the event the incoming AC power is interrupted. Since telecommunications systems often require the backup power supply to provide power to the load for durations ranging from a few seconds to a few days, the implementation of a battery backup system has a significant impact on both the performance and the cost of the power plant.
Traditionally, companies locate telecommunications systems in a central office environment wherein large-capacity power plants provide an energy reserve adequate to power the systems for up to a few days. A power plant based on a DC-bus architecture usually contains a rectifier that processes the incoming AC power and produces therefrom DC power that is applied to a DC battery bus. The power plant further contains a number of batteries, coupled to the DC battery bus, that provide the energy reserve in the event the incoming AC power is interrupted. The power plant provides power to a number of isolated DC--DC converters, typically board mounted power supplies coupled to the loads, that scale the DC power of the DC battery bus to DC power of specific, well-regulated voltages as required by the particular loads.
The rectifier includes a power factor correction circuit that processes the incoming AC power and produces therefrom high voltage DC power. The rectifier further includes an inverter that generates high frequency AC power from the high voltage DC power, for transmission across an isolation transformer. The rectifier still further includes a rectifier circuit and a filter circuit that convert the high frequency AC power into DC power suitable for coupling to the DC battery bus. During a normal mode, the DC power provided to the DC battery bus by the rectifier is used to power the loads and to charge the batteries.
Each isolated DC--DC converter includes an input filter circuit and an inverting circuit that produce high frequency AC power from the DC power on the DC battery bus for transmission across an isolation transformer. The isolated DC--DC converter further includes a diode rectifier circuit and a filter circuit that rectifies the high frequency AC power to produce DC power of a specific, well-regulated DC voltage for output to the load.
Power plants employing the above described DC-bus architecture have the advantages of relatively high system reliability and good decoupling between the various units of load equipment. Because the rectifiers and isolated DC--DC converters are coupled to the DC battery bus, however, this architecture requires many components and power conversion stages and is thus inefficient, bulky and expensive. Additionally, power plants based on the DC-bus architecture expose the power components contained therein to relatively high voltage and current stresses caused by voltage and current variations in the DC battery bus. While the DC-bus architecture remains suitable for spacious central office environments, remote switching equipment, such as those located within the tight confines of wireless base stations, would benefit from a more efficient power architecture requiring fewer components.
Another power architecture currently employed in the telecommunications industry attempts to overcome some of the disadvantages discussed above by eliminating the DC battery bus. In this case, the rectifier circuit and filter circuit of the above described rectifier may be eliminated. The rectifier thus includes a power factor correction circuit that processes the incoming AC power to produce high voltage DC power. The rectifier further includes an inverter that takes the high voltage DC power and generates therefrom high frequency AC power for transmission across an isolation transformer. Since the DC battery bus is no longer available, the batteries are directly coupled, via a DC--DC battery charger/inverter, to the high voltage DC power output of the power factor correction circuit.
Further, the isolated DC--DC converters employed by the DC-bus architecture can be replaced by post-regulator circuits, coupled to an AC bus formed by the isolation transformer. The post-regulator circuits convert AC power on the AC bus to DC power for output to the loads. Typically, each post-regulator circuit includes a diode rectifier circuit, a switching circuit and a filter circuit. By replacing the isolated DC--DC converters with the post-regulator circuits, the input filter circuit and the inverting circuit required by the DC-bus architecture can be eliminated.
While power plants based on this architecture contain fewer components and are, therefore, less costly than those based on the DC-bus architecture, a major disadvantage is the cost and size of the DC--DC battery charger/inverter. Additionally, the power plant is relatively inefficient in a battery backup mode wherein DC power from the battery, available at a low battery voltage (typically 24 or 48 VDC), is stepped up to match the high voltage DC power generated by the power factor correction circuitry (typically 400 VDC).
Accordingly, what is needed in the art is a system for providing backup power that overcomes the disadvantages of the power architectures described above and is thus suitable for use with emerging remote telecommunications systems such as small wireless base stations.